I have an idea to convert a Nerf Firefly into an energy weapon looking Kriss Vector and have a few questions/ideas I'd like to bounce off of more knowledgeable people.

Arduino to be used (unless there are other suggestions and reasoning why):
Arduino Diecimila (grandfather of the Uno)

What I'd like to do is the following:
Have a light (LED, unsure if I'll use 1 small one or a 3/5W one) that either lights up a clear 1 foot barrel. I've been looking at the local hardware stores and it seems they only have flexible clear tubing rather then something rigid. I'm not sure how much of the light will be diffused out of the clear plastic, so I was wondering if a regular 1 foot tubing could work with something on the end to allow people to see that it lights up when the trigger is pressed.

In the two opening gaps near the butt stock of the gun I was thinking of putting an 3 or 4 7-segment LED on one side to act as a pretend virtual counter, with the other side either mirroring it or just having a clear plastic covering it with a light illuminating it. There is no where else on the Nerf gun to place an LED ammo counter as I want to be able to take it apart as shown in the pictures below.

I was also thinking of installing a pizo or a buzzer to indicate/playback an audio track/noise/sound when the device is fired and when it's "empty".

I'd also like to have when the device is "empty" to have some kind of spring or mechanism that is illuminated and ejects out of the back. Requiring someone to push it back in to reset the ammo. Not quite sure what to use with that.

Where the 2 AA battery pack that's built into it I was thinking of replacing it with a single 9V battery pack/holder to supply the Arduino with enough power (and not take up a bunch of space).

I don't have to worry about capturing the trigger being pressed as a limit switch (Or a contact switch, been a little while with component part names) is already wired. I'd just need to feed it into a digital in. Same goes with the on/off switch, it's already wired in.

Here are some pictures of the Nerf Firefly at it's current un-assembled state:

You could perhaps look at an mp3 shield for storing/playback of sounds. I know you have a Diecimila, but I especially like the nano's mp3 shield. It looks slim and small enough that it along with the nano could fit easily into the gun and it has its own speaker and stereo jack if you need a larger speaker.

Well my goal to make it sort of a Blue energy theme is going to go out the window. It seems blue 7 segment LEDs are about 5$ each where I can get a red or green one instead for about 1-2$ tops. I'm not sure if I should go the red or oranage-red route or go with green.

Only thing I haven't gotten figured out is my amplifier (the 3W LED sort of needs more current then the Arduino can supply, though I'm deciding between a transistor and an amplifier) and the clear plastic tubing.

Suggestions on either, more specifically the clear plastic tubing would be a great help.